Subduction recycled components can be incorporated into the mantle through aqueous solution/melt metasomatism; however, tracing the source and nature of metasomatic agents, as well as reconstructing the melting reactions of metasomatic mantles, has consistently posed significant challenges. In this work, we performed an extensive study involving petrology, geochronology, mineral chemistry, geochemistry including Sr-Nd-Pb-Hf isotopes, and numerical modeling on the newly discovered high-Mg diorites in the northeastern Tibetan Plateau to unravel their source reactions between subducting components and the mantle wedge. Zircon U-Pb data reveals that three diorites crystallized at similar to 260 Ma, synchronous with the subduction of the PaleoZongwulong oceanic slab. These rocks show magnesian characteristics of amphibole and biotite, and most of plagioclase cores produce intermediate anorthite contents (An(36-49)). The variable Sr-87/Sr-86(i) ratios ranging from 0.70656 to 0.7094 and most epsilon(Hf)(t) values between-4.1 and + 4.7, but homogeneous epsilon(Nd)(t) values from-5.4 to-2.3 indicate the diorites are derived from an enriched mantle source. The observed enrichment in large ion lithophile elements and depletion in high field strength elements further indicate the characteristics typical of arc igneous rocks. High Th/Nb ratios (0.54-1.37) and Th/Yb ratios (2.42-4.7), alongside low Sr/Th ratios (24.51-59.83) and narrow Pb isotopic variations (Pb-206/Pb-204(i) of 18.09-18.34, Pb-207/Pb-204(i) of 15.59-15.63 and Pb-208/Pb-204(i) of 38.14-38.37), imply the presence of sediment components in the mantle source. Pyroxenites have been identified as their potential source, as indicated by whole-rock chemistry (e.g., high 10000*Zn/ Fe ratios). Numerical modeling suggests that these diorites formed through the addition of similar to 1 % aqueous solutions and 6 %-20 % hydrous melts into the mantle wedge. Therefore, the high-Mg diorites discovered in the northeastern Tibetan Plateau provide valuable insights into the interactions between the crust and mantle, which are associated with slab subduction during the late Paleozoic era.

Regional heat flow provides a direct surface indication of the thermal state and energy balance of the lithosphere. Heat flux in the Tibetan Plateau remains poorly studied due to the lack of adequate information on heat flow. In this study, we investigated granitoids from the Gonghe-Guide district located in the NE Tibetan Plateau, which have important significance as hot and dry rocks with potential for geothermal resources. Samples from granitoid rocks as well as felsic dikes were collected from this area, and their geochemical data were combined with regional geophysical and drilling core data to evaluate a high-heat-flow anomaly. Our data show that granitoid rocks, including granodiorite, monzogranite, and syenogranite, crystallized at ca. 253−240 Ma, while felsic dikes formed ca. 230 Ma. The former were emplaced during the oceanic subduction process, whereas the latter formed in the syncollisional stage associated with the closure of the paleo-Zongwulong Ocean. Geochemically, these granitoid rocks are metaluminous to slightly peraluminous, with an average differentiation index (DI) value of 80, and they are classified as weakly to moderately fractionated I-type granites. The felsic dikes are peraluminous with high DI values (average of 95), typical of highly fractionated I-type granites. In terms of their high K and especially U and Th abundances, the calculated radioactive heat generation produced by the granodiorite, monzogranite, syenogranite, and felsic dikes is 1.85, 2.91, 6.85, and 3.02 μW/m3, respectively. Their moderate to high heat production generates a local heat-flow anomaly of 14.8−22.2 mW/m2 above the regional value of subduction zones, accounting for 11%−18% of the total regional heat flow. In combination with regional magnetotelluric data, the high-heat-flow anomaly may be attributed to an additional heat-flow contribution from a partial melt layer beneath this region. Furthermore, there is a significant positive correlation between the radioactive heat generation and magmatic fractionation, indicating that the enrichments of heat-producing elements are controlled by fractional crystallization and subsequently source composition. The granitoid rocks with high heat generation correspond to the large-scale intermediate-felsic magmatism during the subduction stage. We propose a model wherein a continuous subduction process during the closure of the paleo-Zongwulong Ocean and protracted cooling and crystallization processes resulted in the enrichment in heat-producing elements.

The polarity of Early Paleozoic ocean-continent transformation in South Altun has been an issue recently.However,detailed petrological evidence for the exhumation of the deep subducted continental crust is still lacking.In this paper,it researches petrological,geochemical,zircon U-Pb chronological and Lu-Hf isotopic characteristics of the northern Manya complex,to discuss its source and tectonic environment,and reveal magmatic response to the Early Paleozoic tectonic evolution.The 458-420 Ma granites have similar material source and magmatic source,resulting from the similar ranges of ε Hf(t)and tDM2 values,and shoshonitic characteristics such as rich in alkali and K,and lack of Ti and Fe.The 458-453 Ma granites were formed by decompression melting of deep-subducted continental crust,which were transported to the upper crust by exhumation.The 451-420 Ma granites were product of partial melting of lower crustal materials triggered by underplating of mantle-derived magma in a post-collisional extensional environment.Thus,exhumation of the deep-subducted continental crust completed at<453 Ma,and the orogenic belt were in late orogenic post-collisional environment at<451 Ma.

Early Triassic granitoids are widespread in the northwestern West Qinling Orogen, China, but their petrogenesis and geodynamic implications remain unclear. In this study, we integrated new field and petrological observations, mineralogical compositions, zircon U-Pb dating, Hf isotopic and whole-rock geochemical analyses for the early Triassic granitic pluton in the Daheba area to determine its magma source and geodynamic scenario. The pluton is composed of granodiorite and syenogranite and carries microgranular enclaves (MEs) which formed at ca. 253-249 Ma. The granitoids show wide SiO2 contents of 63.73-77.49 wt% (av. 69.89), high K2O contents of 3.4-5.4 wt% (av. 4.1) and moderate Mg# of 16-51 (av. 36), belonging to high-K, calc-alkaline I-type granites. These rocks have high radiogenic but uniform Hf isotopic compositions with 176Hf/177Hf and epsilon Hf(t) of 0.282511-0.282658 and -3.85 - +1.25, respectively. The MEs hosed within the granite are characterized by high Mg# of 35-58 (av. 46) and variable epsilon Hf(t) of -4.64 - +9.35, which likely represent a hybridized melt derived from a slab-modified mantle and lower crust. In combination with coeval magmatic rocks in the western Gonghe-East Kunlun area, we propose a genetic model where mafic magmas derived from an enriched mantle and underplated beneath the overlying lower crust are considered to have produced the high-K felsic magma. Further, the hybridized melt ascended to shallower crustal levels to generate a series of rocks ranging from dioritic MEs to granodiorite to syenogranite. Mass balances modeling suggests that the generation of these rocks involved 36 % of the lower crustal-derived melt and 64 % of the SCLM (R2 = 0.9). Our new data, in tandem with published results suggest that the Daheba pluton formed during the subduction stage of the Paleo-Tethyan Ocean and that a local extensional episode occurred at 253-249 Ma in the western Gonghe area.

The Western Qinling Orogen is marked by secular Triassic magmatism, a thorough understanding of the mechanism of which could provide critical insights into the reconstruction of the Palaeo-Tethys tectono-magmatic activity. Here, we present new geochemical, geochronological and Lu-Hf isotopic data for three batholiths and review regional data. These batholiths have similar rock assemblages (mainly granodiorite and monzogranite), which are characterized by dominantly plagioclase, quartz, and K-feldspar, subsequently amphibole and biotite. Zircon U-Pb data reveal that they represent the long-duration magmatism during the Triassic (ca. 251–223 Ma). Mineralogical characteristics and geochemical affinities manifest that these rocks in the Zeku district can be explicitly delineated as high-K, calc-alkaline, weakly fractionated I-type granites. They yield significantly negative εHf(t) values ranging from −12.81 to −1.26 with old two-stage mantle depleted model ages between 2054 and 1319 Ma. In tandem with Th/Nb (0.98), Th/La (0.39) and La/Nb (2.40) ratios and moderate pressure conditions (ca. 7–10 kbar), the studied granites were derived from partial melting of the Middle Paleoproterozoic to Middle Mesoproterozoic lower crust source region with minor mafic hydrous magma addition. Our new understandings, in conjunction with the temporal-spatial distribution characteristics of magmatism in the West Qinling Orogen, as well as the regional tectonic evolution, suggest that the superimposed orogeny evolved from the northward subduction of the Palaeo-Tethys Ocean (264–225 Ma) through syn-collision (225–215 Ma) to post-collision (beginning at ca.215 Ma) between the North China Craton and South China Block. In this scenario, at the convergent continental margin, the oceanic plate may have undergone melting producing the melts parental to the Zeku granites.

Analytical methods, supporting Figures S1-S10 and Tables S1-S9.

南阿尔金造山带是中国西北地区重要的俯冲—碰撞杂岩带.笔者等对茫崖地区出露的闪长岩开展岩石学、地球化学、锆石U-Pb年代学和Lu—Hf同位素地球化学研究,探讨其岩石成因和成岩时的构造环境.研究表明,茫崖闪长岩亏损Nb、Ta、Ti、P、Th、U、HREEs、Ba、Sr等元素,富集Rb等大离子亲石元素及LREEs,显示与俯冲相关岛弧岩浆岩相似的地球化学特征.样品的锆石U-Pb年龄为494～461Ma,εHf(t)为0.01～3.90,tDM2为1496～1447 Ma,少量εHf(t)为负值(-2.22～-0.03),tDM2为1453～1254 Ma,指示其物质来源以中元古代(1453～1254 Ma)新生地壳物质为主,混合少量中元古代(1496～1447 Ma)古老地壳物质.综上,该期岩浆活动是幔源岩浆的底侵作用导致下地壳熔融的产物,指示南阿尔金造山带在＜494 Ma进入深俯冲陆壳断离—折返阶段,同时伴随着大规模幔源岩浆的底侵作用,茫崖闪长岩是深俯冲陆壳断离后折返作用的岩浆活动响应.

The South Altun orogenic belt is an important subduction-collision complex belt in northwest China, located between the Tarim and the Qaidam basins. Its early Paleozoic tectonic evolution has been one of the research hotspots in recent years. However, the timing of oceanic crust subduction has been controversial. In this paper, we study the petrology, geochemistry, zircon U-Pb chronology and zircon Lu-Hf isotope geochemistry of the Manya quartz monzonite, and discuss its petrogenesis and the tectonic environment. The samples show high alkali, potassium-rich, low-titanium, iron-poor and Nd-Ta-Ti anomalies similar to shoshonitic rocks. The quartz monzonites were generated between 511 Ma to 495 Ma, and the values of epsilon(Hf) (t) mainly range from -3. 51 to -0. 08, with some positive values ranging from 0. 04 to 1. 69. Based on our research, we infer that the subducting oceanic crust released large amounts of water when arriving at amphibolite facies boundaries, and triggered the mantle wedge peridotite hornblende metasomatism. Due to the dragging of the subducting oceanic crust, the temperature of the mantle wedge rose, causing the melting of the hornblende metasomatized peridotite, which triggered the partial melting of upper crust materials. Finally, crustal melts mixed with smaller mantle melts to form quartz monzonite. The similar to 500 Ma granites are petrological response to transition from oceanic island arc environment to active continental margin. Thus, the southern Altun oceanic crust may have begun subducting at around 517 Ma.

The Gonghe geothermal basin is situated in the westernmost part of the western Qinling orogen and possesses the supreme potentials to explore and develop hot dry rock (HDR) geothermal resources in China. The basal rock of HDR reservoir in Gonghe basin is composed of granitoids. In this contribution, in order to constrain the formation mechanism of the Gonghe HDR, granitic samples from outcropping have been collected and drilling core samples data from the archives also been compiled. The studied results show that the obtained zircon U-Pb ages of 255.1 +/- 1.9 Ma and 253.9 +/- 2.6 Ma for granodiorite and monzogranite, respectively. All granitoids from both outcropping and drilling core have the similar rock associations and their major and trace elements possess the consistent evolved patterns, such as relative enrichment of LILEs (e.g., K, Rb), depletion of HFSEs (e.g., Nb, Ti), and negative Eu anomalies (0.32-0.66), indicating that they share the same magma sources and evolutional processes. And they have the affinity of I-type granites. They were derived from the mixture of partial melting of metabasaltic rocks in the lower crust and a small amount of mantle-derived magma and formed in a subductionrelated setting relative to the southward subduction of the Zongwulong oceanic crust beneath the west Qinling terrane. The heat production values of rocks around the Gonghe basin were calculated and all basal granitic rocks ranges from 0.35 to 8.51 mu W/m3, yielding an arithmetic mean value of 1.97 mu W/m3, indicating that the radioactive heat generation capacity of granitoids in the Gonghe basin is slightly lower. The HDR reservoir in the Gonghe basin was probably due to an allied thermal effect of the radiogenic heat production in the thickening continental crust and the heat contributed by a deep magma chamber below the basin. The early Triassic granitoids with a higher thermal conductivity serve as the conductive medium of the geothermal heat; whilst the sedimentary rocks marked by lower thermal conductivity above the granitic batholiths act as the reservoir cap. This contribution provides a relatively rational understanding for the mechanism of the HDR reservoir in Gonghe geothermal basin from the petrological and geochemical perspectives, which is conducive to the geothermal potential assessment and estimation, and to-be implementation of the Enhanced Geothermal System demonstration project in China.

The Xiangpishan complex in the Zongwulong‐Qinghainanshan Tectonic Belt, Northeast (NE) Tibetan Plateau, is a composite concentric pluton consisting of a felsic core (granodiorite) surrounded by quartz diorite in the middle to diorite and minor gabbro at the margin with locally less volume of monzogranite. Many dioritic enclaves are unevenly distributed within host granitoids. We evaluate the petrogenesis of the complex by geochemical, geochronological, and Hf isotopic data in tandem with regional data in the belt. The results show that felsic rocks were emplaced during the Late Permian (ca. 262–256 Ma); whilst gabbros yielded a younger age of ca. 249 Ma. As the hybrid phase from mixing between felsic and mafic magmas, enclaves and diorites have analogous ages (ca. 257–254 Ma) to both. Zircons from gabbro and enclaves are marked by higher εHf(t) value up to +1.82; whilst granodiorites have lower εHf(t) value of −5.48, consistent with hybrid diorites possessing intermediate εHf(t) values of −3.14 to 0.34. Furthermore, the quantitative calculation from Mass Balances Modelling suggests that the mass of mafic magma (ca. 67%–79%) is involved to achieve the hybridization. Geochemically, these rocks crystallized from calc‐alkaline magma with different sources, but demonstrated consistent arc‐like signatures, as they are enriched in large‐ion lithophile elements and light rare earth element (LREE), and depleted in high‐ field‐strength elements and heavy rare earth element (HREE). Besides, they present negative Nb–Ta anomalies together with significant P and Ti troughs. Finally, an evolutional model has been proposed that the asthenosphere‐lithosphere interaction played an important role during the emplacement of the complex, where the limited volumes of mantle‐derived melt act as the suppliers of heat and mass (mainly volatile components) to induce partial melting of the juvenile mafic lower crust and mixed (or mingled) with the produced crust‐derived magma during the oceanic subduction, which led to the generation of diorites as well as mafic microgranular enclaves.

Precise timing of granitoids and constraints of their magma sources are critical to understanding the subduction–collision tectonic evolution of the Altun orogenic belt (AOB), a vital part of the Qinghai-Tibet plateau in northwestern China. We provide in-situ zircon U–Pb age, Hf isotopic composition and whole-rock geochemistry of the Yusupualeke granitic pluton in the South Altun orogenic belt (SAOB), an integral unit of the AOB, to determine the tectono-magmatic evolution of the SAOB at early Palaeozoic. The Yusupualeke granitic pluton comprises the medium-coarse grained porphyritic monzogranite and medium-fine grained granodiorite. The monzogranite sample yielded a weighted mean 206Pb/238U age of 476.8 ± 3.6 Ma (MSWD = 0.59), while the granodiorite yielded a weighted mean 206Pb/238U age of 453.2 ± 4.7 Ma (MSWD = 0.013). Zircon U–Pb ages suggest that the subduction–collision process of the SAOB remained from the middle stage of the early Palaeozoic to the end. Both of the studied granitoids belong to metaluminous to weakly peraluminous series and show typical I-type granite characteristics with depletions in Ba, Nb, Sr, P, and Ti, and enrichments in light rare earth elements (LREEs), Rb, Th, K, and slightly negative Eu anomalies. Based on the geochronological data and regional geological background, we believe that the porphyritic monzogranites were formed during the northward subduction process of the South Altun ocean (SAO), while the granodiorites were formed during the tectonic regime transition stage. Besides, combing the previous research achievements with our newly obtained data, we put forward a new division and geodynamic model of the early Palaeozoic tectono-magmatic evolution for the South Altun orogenic belt.

The western Gonghe basin in the NE Tibetan Plateau, witnessed extensive magmatism during the Triassic, whereas only few magmatic flare-up events occurred during the Permian. Understanding the geodynamic setting of these magmatic pulses is important in the reconstruction of the Paleo-Tethys tectonic history. In this contribution, we present in-situ zircon U-Pb geochronological and Lu-Hf isotopic data, as well as whole-rock major and trace elements data from monzogranite and syenogranite dyke in the western Gonghe region to constrain their petrogenesis and tectonic implications. Zircon U-Pb data show that the monzogranite (253-260 Ma) and syenogranite dyke (247-261 Ma) were formed during the Late Permian, rather than the Jurassic as presumed in previous studies. Mineralogical characteristics and geochemical affinities reveal that these rocks are high-K calcalkaline, metaluminous to weakly peraluminous (ASI = 0.95-1.02), moderately-highly fractionated (DI = 81-95) I-type granites. The major and trace element characteristics (including Mg#, Ni, Cr, Zr/Hf, Nb/Ta, and Th/U contents), together with the zircon epsilon Hf(t) values (-5.90 to 1.22, TDMC = 845-1250 Ma) and 176Hf /177Hf ratios (0.282481 to 0.282674) suggest that the magmas were derived through partial melting of the Early Mesoproterozoic metagreywacke in the lower crust with minor juvenile crust addition. Extensive fractional crystallization of plagioclase and subordinate K-feldspar as well as apatite is inferred. Our findings in this study, in conjunction with those from previous studies, suggest that the magmatic flare-up event during the Late Permian in the western Gonghe area is related to local extension concomitant with the break-off of the subducting slab associated with the northward subduction of the Paleo-Tethys oceanic lithosphere.

[研究目的]玉苏普阿勒克塔格花岗岩体位于阿尔金造山带南部茫崖蛇绿混杂岩带内,主要由中粗粒似斑状黑云二长花岗岩及中细粒含斑黑云二长花岗岩组成.玉苏普阿勒克塔格岩体的形成时代、成因类型和岩浆物质来源尚不明确,制约了我们进一步认识该岩体形成的地球动力学背景以及南阿尔金造山带早古生代构造演化过程.[研究方法]因此,本文对玉苏普阿勒克塔格岩体进行了岩石学、锆石U-Pb年代学、全岩地球化学、黑云母矿物化学及Hf同位素组成等方面的研究.[研究结果]锆石U-Pb年代学研究结果表明该岩体中粗粒似斑状黑云二长花岗岩的锆石U-Pb加权平均年龄为451～447 Ma.结合前期工作获得该岩体中细粒含斑黑云二长花岗岩的年龄(430～423 Ma),笔者认为玉苏普阿勒克塔格花岗岩体属于早古生代岩浆活动的产物.黑云母矿物化学研究结果表明,玉苏普阿勒克塔格岩体形成于温度较低压力较高环境.根据玉苏普阿勒克塔格岩体两期花岗岩的矿物组成、全岩地球化学特征及形成的物理化学环境,认为该岩体属于I型花岗岩.Hf同位素组成研究结果表明,玉苏普阿勒克塔格岩体两期花岗岩具有相似的Hf同位素组成,暗示它们具有相似的物质来源:源岩以新生地壳的部分熔融为主,在侵位过程中经历了部分古老地壳物质的混染.[结论]综合玉苏普阿勒克塔格花岗岩体的形成时代、成因类型、物质来源,结合区域构造演化资料,本文认为玉苏普阿勒克塔格岩体形成于与南阿尔金洋北向俯冲有关的活动大陆边缘环境.

The Altun orogenic belt (AOB) was the site of complex subduction of oceanic crust and continental collision during the Paleozoic. The North Altun ophiolitic mélange belt (NAB) is a one of the key tectonic units of the AOB and contains abundant subduction- and collision-related rocks. In this paper, we report the petrography, zircon U–Pb ages, geochemistry, and zircon Hf isotopes of the Bashikaogong S-type granitic rocks from the North Altun ophiolitic mélange belt (NAB) to constrain their petrogenesis and tectonic setting. The granitic rocks consist of three types of granites, i.e., (1) gray, medium- to coarse-grained porphyritic granite; (2) gray, medium-grained granite; and (3) pink, medium- to coarse-grained granite. Zircon U–Pb dating yielded ages of 483–477, 458–453, and 447–445 Ma for type 1, type 2, and type s3 granites, respectively. All the three types of granites share similar strongly peraluminous (A/CNK > 1.1), contain muscovite mineral, have K2O/ Na2O ratios of > 1, and display negative zircon εHf(t) values, which are similar to typical S-type granites. On the basis of our data and results of previous studies, we infer that type 1 granites (483–477 Ma) are related to subduction of North Altun oceanic lithosphere, type 2 granites (458–453 Ma) are syn-collision granites related to continental collision between the Central Altun and Dunhuang Blocks, and type 3 granites (447–445 Ma) are from the late-collision stage. The Bashikaogong S-type granitic rocks recorded early Paleozoic subduction and collision in the North Altun region and were generated by the partial melting of the protolith of the metasedimentary Paleoproterozoic–Mesoproterozoic basement in the CAB due to the collapse of the overthickened subduction orogen.

AbstractThe South Altyn Orogenic Belt (SAOB) is one of the most important orogenic belts in NW China, consisting of the South Altyn Continental Block and the Apa–Mangya Ophiolitic Mélange Belt. However, its Palaeozoic tectonic evolution is still controversial. Here, we present petrological, geochemical, zircon U–Pb and Lu–Hf isotopic data for the Mangya plutons with the aim of establishing the Palaeozoic tectonic evolution. We divide the Early Palaeozoic magmatism in the Apa–Mangya Ophiolitic Mélange Belt into four episodes and propose a plate tectonic model for the formation of these rocks. During 511–494 Ma, the South Altyn Ocean (SAO) was in a spreading stage, and some shoshonite series, I-type granitic rocks were generated. From 484 to 458 Ma, the oceanic crust of the SAO subducted northward, accompanied by large-scale magmatic events resulting in the generation of vast high-K calc-alkaline series, I-type granitic rocks. During 450–433 Ma, the SAO closed, and break-off of the subducted oceanic slab occurred, with the generation of some high-K calc-alkaline series, I–S transitional type granites. The SAOB was in post-orogenic extensional environment from 419 to 404 Ma, and many A-type granites were generated.

The Altun orogenic belt, located on the northern margin of the Tibetan Plateau, records the assembly and breakup of the Rodinia supercontinent. In this paper, we report the petrography, zircon U–Pb ages and Hf isotope data, and bulk geochemistry of the Hongliugou alkali feldspar granites from the Altun orogenic belt to constrain their petrogenesis and tectonic implication. Zircon U–Pb dating yielded ages of 857–851 Ma, interpreted as the emplacement ages of the granites. The granites are metaluminous; have high SiO2, K2O, and rare‐earth element (REE) contents; low CaO and P2O5 contents; high FeOt/MgO ratios; and high 10,000 × Ga/Al values. They show marked depletion in heavy REEs, enrichment in light REEs, and pronounced negative Eu anomalies. These rocks are enriched in high‐field‐strength elements, depleted in Ba, Sr, P, and Ti, and lack Nb and Ta anomalies. These petrological and geochemical characteristics are consistent with those of A‐type granites. The samples plot in the A1‐type field in a discrimination diagram for A‐type granites. Zircon εHf(t) values vary from +1.76 to +7.40 with two‐stage Hf model ages of 1.27 to 1.63 Ga, implying that the granites were derived mainly from juvenile crust. On the basis of these and previous results, we propose that the Hongliugou alkali feldspar granites formed in an intraplate rift setting related to the initial breakup of Rodinia.

通过锆石LA-MC-ICP-MS Lu-Hf同位素分析,结合前人地球化学资料对舒家店地区中酸性侵入岩进行了研究.主量、微量元素地球化学特征表明区内侵入岩为准铝质,具有岛弧岩浆岩的特征,区内岩浆的演化可能经历了同化混染与分离结晶(AFC)过程.通过分析,我们认为舒家店地区的早白垩世岩浆活动可能与早白垩世初太平洋板块的斜向俯冲相关,侵入岩的形成演化受到了区域构造应力场的制约.Hf同位素分析及计算结果表明,除两个继承性锆石核外,本区侵入岩锆石的εHf(t)均为负值,橄榄安粗岩系列侵入岩的εHf(t)值为-8.6～-4.1,高钾钙碱性系列εHf(t)值为-13.4～-4.7.与高钾钙碱性系列相比,橄榄安粗岩系列侵入岩的εHf(t)更接近球粒陨石演化线.从εHf(t)值的变化特征来看,两个系列侵入岩均为来源于富集地幔,且在演化过程中混染了地壳物质,而高钾钙碱性系列在这个过程中混入了更多的地壳物质.

安徽铜陵矿集区出露的侵入岩可划分为高钾钙碱性和橄榄安粗岩系列,作为铜陵7大矿田之一的焦冲地区是否也存在两个系列侵入岩?它们的时代及成因与整个铜陵地区的侵入岩是否相同?这些问题目前仍不清楚.本文选择铜陵焦冲矿田的侵入岩开展了岩相学、岩石地球化学、LA-ICPMS锆石U-Pb定年及原位Hf同位素地球化学研究.结果表明,焦冲矿田也存在高钾钙碱性系列和橄榄安粗岩系列侵入岩,前者的主要岩石类型为石英二长闪长岩、花岗闪长岩,后者为辉石二长闪长岩.LA-ICPMS锆石U-Pb定年结果显示,高钾钙碱性系列侵入岩年代与铜陵地区其他矿区同类岩石年代相同,约为142 Ma;而橄榄安粗岩系列侵入岩年代比铜陵地区其他矿区同类岩石年轻,约为136 Ma.总体上看,铜陵地区两个系列侵入岩具有多期次侵位的特征.焦冲高钾钙碱性系列侵入岩含有较多的老的继承性锆石,说明本区古老地壳卷入了岩浆形成过程.结合铜陵地区侵入岩的特征和焦冲矿田侵入岩岩石地球化学研究结果,笔者认为,焦冲矿田两个系列侵入岩成因与铜陵地区侵入岩相似,即橄榄安粗岩系列侵入岩是来自莫霍面附近深部位岩浆房富碱基性岩浆结晶分异后的产物,而高钾钙碱性系列侵入岩是深位岩浆房分异后的岩浆与浅位岩浆房长英质岩浆混合后的产物.

Objective The Dunhuang Block is located in the conjunction area of the Tarim Craton, Central Asian Orogenic Belt, North China Craton, and Tethyan tectonic domain, and is traditionally regarded as a Precambrian crystalline basement block. However, recent research concluded that

南阿尔金造山带位于柴达木盆地和祁连-昆仑造山带之间,是一条重要的大陆俯冲-碰撞造山带,带中分布的大量早古生代花岗岩蕴含着造山带构造演化的重要信息.茫崖A型碱长花岗岩对限定南阿尔金进入造山后伸展环境的时限以及壳幔相互作用具有指示意义,然而该岩体的成因类型、物质来源和形成的构造环境缺乏详细研究.因此,本文利用岩相学、岩石地球化学、LA-ICP-MS U-Pb年代学和Lu-Hf同位素分析对碱长花岗岩进行系统的研究,并探讨岩浆活动对造山带构造演化的响应.碱长花岗岩显示高硅、富铁、富碱、贫钙和镁的特点,并强烈亏损Ba、Sr、P、Eu和Ti,属于A2型花岗岩;岩体的结晶年龄为403～424Ma,是中—新元古代新生地壳(新生长英质物质或钙碱性花岗岩类)部分熔融的产物,岩浆源区可能存在少量富Ca斜长石残留相;南阿尔金造山带在424M a之后进入造山后的伸展环境,不同块体之间的均衡调整导致深部幔源物质持续上涌,造成地壳的部分熔融,形成了这一期A型花岗岩.